This invention relates in general to the field of information storage and more particularly to a method and circuitry for acquiring a signal in a read channel.
As computer hardware and software technology continues to progress, the need for larger and faster mass storage devices for storing computer software and data continues to increase. Electronic databases and computer applications such as multimedia applications require large amounts of mass storage capacity, such as hard disk drive storage capacity.
To meet these ever increasing demands, hard disk drives (HDDs) continue to evolve and advance. Some of the early disk drives had a maximum storage capacity of five megabytes and used fourteen inch platters, whereas today""s HDDs commonly have a storage capacity in the gigabyte range and use 3.5 inch platters. The increase in HDD storage capacity corresponds with increases in the amount of data stored per unit of area, or areal density. As such, HDD areal density has dramatically accelerated along with the increase in storage capacity. For example, in the 1980""s, areal density increased about thirty percent per year, while in the 1990""s annual areal density increases have been around sixty percent. Increases in areal density is important because the cost per megabyte of a HDD is inversely related to its areal density.
In general, mass storage devices and systems, such as HDDs, include a magnetic storage media, such as rotating disks or platters, a spindle motor, read/write heads, an actuator, a pre-amplifier, a read channel, a write channel, a servo circuit, and control circuitry to control the operation of the HDD and to properly interface the HDD to a host or system bus. The read channel, write channel, servo circuit, and memory may all be implemented as one integrated circuit that is referred to as a data channel. The control circuitry often includes a microprocessor for executing control programs or instructions during the operation of the HDD.
An HDD performs write, read, and servo operations when storing and retrieving data. These operations may occur in virtually any order. As the disk platters are moving, the read/write heads must align or stay on a desired track. This is accomplished by a servo operation using the servo circuit and the control circuitry. In a servo operation, a servo wedge is read from the disk. Generally, each sector includes a corresponding servo wedge. A sector generally has a fixed data storage capacity, such as 512 bytes of user data per sector. A servo wedge includes track identification information and track misregistration information, which may also be referred to as position error information. The position error information may be provided as servo bursts and may be used during both read and write operations to ensure that the read/write heads are properly aligned on a track. The track identification information is used during read and write operations so that a track may be properly identified. The servo circuit is used, while the disk platters are moving, to align the read/write heads with a desired track.
In a write operation, data is transferred from a host interface to its control circuitry. The control circuitry then stores the data in a local dynamic random access memory (DRAM). A control circuitry processor schedules a series of events to allow the data or information to be transferred to the disk platters through a write channel. The control circuitry, along with the servo circuit, moves the read/write heads to the appropriate track and locates the appropriate sector of the track. Finally, the control circuitry transfers the data from the DRAM to the located sector of the disk platter through the write channel. The write channel will encode the data so that the data can be more reliably retrieved later.
In a read operation, the appropriate sector to be read is located and data that has been previously written to the disk is read. A read operation may be needed after having just performed any other operation such as a write operation, a servo operation, or another read operation. Before reading actual user data, the read channel is prepared or conditioned to accurately acquire or read the data provided in the associated sector by performing various operations on fixed data provided in a preamble or header section. The read/write head senses the changes in the magnetic flux of the disk platter and generates a corresponding analog read signal. The read channel receives the analog read signal, processes the signal, and detects xe2x80x9czerosxe2x80x9d and xe2x80x9conesxe2x80x9d from the signal. The read channel processes the signal by amplifying the signal to an appropriate level using automatic gain control (AGC) techniques. The read channel then filters the signal, to eliminate unwanted high frequency noise, equalizes the channel, detects xe2x80x9czerosxe2x80x9d and xe2x80x9conesxe2x80x9d from the signal, and formats the binary data for the control circuitry. Any of a variety of techniques may be used for detecting xe2x80x9czerosxe2x80x9d and xe2x80x9conesxe2x80x9d such as peak detection techniques and partial response, maximum likelihood detection techniques, which are used in synchronously sampled read channels that often use a Viterbi detector for performing maximum likelihood detection. The binary or digital data stored in the sector is then transferred from the read channel to the control circuitry and is stored in the DRAM of the control circuitry. The processor then communicates to the host that data is ready to be transferred.
As mentioned above, before a read operation actually takes place, the read channel must be properly prepared or conditioned to accurately acquire a read signal which contains the user data stored in the sector to be read. In addition to containing user data, each sector contains a preamble section, also called a header section, that includes fixed data or a fixed signal that allows the read channel to prepare and condition itself to read user data stored in the corresponding sector. The preamble section is generally provided at each sector and may be provided at the first of a sector, at various points throughout a sector, or anywhere in a sector. This varies from manufacturer to manufacturer. The preamble section may include information used to perform such functions as AGC to prepare the read channel to acquire the read signal. For example, the preamble section may contain a series of magnetic transitions that allow the read channel to adjust its gain and sampling signal synchronization rate or clock so that the read channel can detect a synchronization field or byte and correctly acquire the read signal which contains the user data.
Overall HDD capacity suffers due to the presence of the preamble sections. Each byte dedicated to the preamble sections corresponds to a reduction in the overall HDD storage capacity available for storing user data or information.
From the foregoing it may be appreciated that a need has arisen for a method and circuitry for accurately acquiring a signal in a read channel that requires a smaller preamble section and hence increases overall HDD storage capacity. The present invention recognizes that the size of the preamble section is related to the length of time it takes for the read channel to acquire a read signal and, hence, provides a method and circuitry for acquiring a signal in a read channel in an expeditious manner. In accordance with the present invention, a method and circuitry for acquiring a signal in a read channel are provided which substantially eliminate the disadvantages and problems outlined above.
According to an aspect of the present invention, a method for acquiring a signal in a read channel having an equalizer includes performing an automatic gain control sequence; performing a phase locked loop sequence that includes performing a fast phase locked loop step, the fast phase locked loop step including bypassing the equalizer; and performing a synchronization search sequence.
The present invention provides various technical advantages. A technical advantage of the present invention includes increased overall HDD data capacity. Another technical advantage of the present invention includes fast automatic gain control and fast sampling signal generation to reduce the time required to acquire a signal in a read channel. Yet another technical advantage of the present invention includes the capability to acquire a signal in a minimal number of steps. Still yet another technical advantage of the present invention includes programmable circuitry that allows for the optimization or minimization of the time needed to prepare a read channel to acquire a read signal. These technical advantages may be attributed, at least in part, to a variety of alternative approaches for more rapidly acquiring a signal, such as, for example, a preamble signal according to the teachings of the invention as more particuarly defined in the claims. Other technical advantages are readily apparent to one skilled in the art from the following figures, description, and claims.